1. Field of the Invention
The present invention relates to a video display apparatus and a video display method capable of displaying video responding to a plurality of types of video signals.
2. Description of the Related Art
In information processing apparatuses for example personal computers, a variety of video display apparatuses such a CRT (cathode ray tube) and a LCD (liquid crystal display) have been used. These information processing apparatuses output a variety of types of video signals depending on manufacturer or model thereof. Therefore, in recent years, an apparatus called multiscan type monitor appeared as a video display apparatus having functions capable of responding to these various video signals.
First, with reference to FIGS. 1 and 2, an explanation is made of a video signal inputted from a conventional information processing apparatus to a video display apparatus. FIG. 1 shows a waveform in one horizontal scanning period. FIG. 2 shows a waveform in one vertical scanning period.
As shown in FIG. 1, respective horizontal scanning periods are partitioned by horizontal synchronizing signals SYNCH of a fixed cycle. One horizontal scanning period comprises a pulse width portion of the horizontal synchronizing signal SYNCH, a back porch portion BPH, a horizontal active portion ACTH, and a front porch portion FPH. The horizontal active portion ACTH is a portion in which video is actually displayed in the horizontal direction on the screen. The back porch portion BPH and the front porch portion FPH are portions displayed as black frames at left and right ends on the screen.
On the other hand, as shown in FIG. 2, respective vertical scanning periods are partitioned by vertical synchronizing signals SYNCV of a fixed cycle. One vertical scanning period comprises a pulse width portion of the vertical synchronizing signal SYNCV, a back porch portion BPV, a vertical active portion ACTV, and a front porch portion FPV. The vertical active portion ACTV is a portion in which video is actually displayed in the vertical direction on the screen. The back porch portion BPV and the front porch portion FPV are portions displayed as black frames at top and bottom ends on the screen.
As shown in FIGS. 1 and 2, a video signal has several timing elements (hereinafter referred to as xe2x80x9ctiming dataxe2x80x9d), and difference in one of timing data makes a difference in type of video signal. For example, in video signals differing from each other in frequency or polarity of horizontal synchronizing signal SYNCH, usually, back porch portion BPH, horizontal active portion ACTH, and front porch portion FPH are also different from each other. It is also true of vertical direction.
Types of video signals differs variously depending on computers or video cards which output video signals. It is believed that there are hundreds of types of video signals. In a multiscan type monitor mentioned above, it is required for any type of video signal inputted thereto to be able to be displayed in proper size and in proper position on the screen. Therefore, formerly, that requirement had been met by the following approaches.
The first approach is as follows: In a factory in advance, a video signal timing data of which are known is actually inputted to a video display apparatus, and adjustments are made in order that video displayed on the screen is of a predetermined size and in a predetermined position, and the values of the adjustments (adjustment parameters) at that time are associated with the type of the video signal and written into a nonvolatile memory or the like. Such adjustments and adjustment value writing process are performed for all of known video signals which are expected to be used. On the other hand, at the time of actual use, type of the video signal inputted from a computer of a user is searched, and adjustment parameters associated with the type of the video signal are read out from the nonvolatile memory and display is performed with these parameters.
The second approach is as follows: At the time of actual use, all of timing data related to the video signal inputted thereto are measured and predetermined operations are made based on these timing data to find adjustment parameters, and display is performed with these parameters. In this case, there is no need to make adjustments in a factory in advance as in the first approach.
However, in the first approach described above, it is necessary to make adjustments of several adjustment parameters for one type of video signal in a factory. Consequently, if there are hundreds of types of video signals to respond to, it is necessary to make adjustments each time switching of video signal to be inputted is performed. A problem of the first approach is that these adjustments require much time and labor. As a countermeasure against this problem, for example, there is a method in which size and position of display area on the screen are detected by a sensor and automatic adjustments are made so that size and position are optimum However, this method requires an automatic adjustment apparatus which could be a cause of increase of production cost.
Also, in the second approach, all of timing data related to the video signal inputted are measured and adjustment parameters are calculated based on these timing data. Therefore, the second approach has a problem that a measurement error leads to lowering of precision of adjustments. In particular, for high frequency and/or a video signal which has a short active portion (point, line or the like), a measurement error may increase. So it is assumed that lowering of precision of adjustments is noticeable. Furthermore, measurement of timing data related to a video signal require considerable time, and the second approach has another problem that it takes long time to display proper video on the screen after a video signal is inputted.
The present invention is made in view of these problems, and the object of the invention is to provide a video display apparatus and a video display method capable of reducing time required to make adjustments in a factory and performing correct and highly responsive video display regardless of types of video signals inputted thereto.
In a video display apparatus or a video display method according to the invention, type of the video signal is detected when a type of video signal is inputted. Using the type detected as a retrieval key, retrieval of timing data stored in advance for respective types of video signals is performed so as to fetch pertinent timing data. Then, adjustment parameters are calculated based on the fetched timing data and video display is performed based on these adjustment parameters. Therefore, time required to make adjustments in a factory can significantly be reduced as compared with conventional method in which adjustment parameters inherent in the apparatus are stored for respective types of video signals and pertinent ones are read out from among these adjustment parameters and used when necessary. Furthermore, processing can be simplified and lowering of precision of adjustments due to a measuring error can be prevented because measurement of timing data is not necessary, as compared with conventional method in which, whenever a new video signal is inputted, all of timing data related thereto are measured and adjustment parameters are calculated using the measured values.
In another video display apparatus according to the invention, adjustment parameters are operated using both timing data acquired by retrieval and characteristics data inherent in the video display apparatus. Therefore, in addition to the above effect, proper adjustment parameters can be obtained taking account of inherent difference among apparatuses due to hardware variation, so that precision of adjustments can further be improved. In to addition, only one set of characteristics data is required for a type of video signal, so that time required for measurement in a factory can be shortened.
In still another video display apparatus according to the invention, when adjustment parameters relating to pertinent type of video signal cannot be obtained as a result of retrieval of the adjustment parameter storing means using the type of the video signal as a retrieval key, the timing data storing means is further retrieved. Then, adjustment parameters are calculated using timing data acquired from the timing data storing means and are additionally recorded into the adjustment parameter storing means, and video display is performed based on these adjustment parameters. On the other hand, when adjustment parameters relating to pertinent type of video signal are obtained as a result of retrieval of the adjustment parameter storing means, video display is performed based on these retrieved adjustment parameters. Therefore, when the same type of signal is again inputted, object adjustment parameters can immediately be obtained from the adjustment parameter storing means. Therefore, retrieval of timing data and operations to calculate adjustment parameters become unnecessary and time from input to display is shortened, so that responsiveness is improved.
In another video display apparatus according to the invention, contents of the timing data storing means can be rewritten based on data supplied from outside. Therefore, the video display apparatus becomes also responsive to a new type of video signal which is not registered at the time when the apparatus is distributed to the market. Also, if there are a plurality of video signals which are of same signal type but having different timing data, the apparatus is capable of responding thereto.
Other and further objects, features and advantages of the invention will appear more fully from the following description.